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Mon, 05 Dec 2022 06:21:38 -0800 (PST) Date: Mon, 5 Dec 2022 09:21:37 -0500 From: Johannes Weiner To: Hugh Dickins Cc: Andrew Morton , Shakeel Butt , Michal Hocko , Roman Gushchin , Yu Zhao , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm: memcg: fix swapcached stat accounting Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: AE6B040016 X-Stat-Signature: fxihup9p4n8f935fn87tujcw37xpb735 X-Spamd-Result: default: False [2.76 / 9.00]; SORBS_IRL_BL(3.00)[209.85.208.50:from]; BAYES_HAM(-0.34)[69.90%]; MIME_GOOD(-0.10)[text/plain]; RCVD_NO_TLS_LAST(0.10)[]; BAD_REP_POLICIES(0.10)[]; TO_DN_SOME(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; DMARC_POLICY_ALLOW(0.00)[cmpxchg.org,none]; DKIM_TRACE(0.00)[cmpxchg-org.20210112.gappssmtp.com:+]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; R_SPF_ALLOW(0.00)[+ip4:209.85.128.0/17]; RCVD_COUNT_THREE(0.00)[3]; R_DKIM_ALLOW(0.00)[cmpxchg-org.20210112.gappssmtp.com:s=20210112]; ARC_SIGNED(0.00)[hostedemail.com:s=arc-20220608:i=1]; PREVIOUSLY_DELIVERED(0.00)[linux-mm@kvack.org]; RCVD_VIA_SMTP_AUTH(0.00)[] X-Rspam-User: X-HE-Tag: 1670250100-250666 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Dec 04, 2022 at 05:01:03PM -0800, Hugh Dickins wrote: > I'd been worried by high "swapcached" counts in memcg OOM reports, > thought we had a problem freeing swapcache, but it was just the > accounting that was wrong. > > Two issues: > > 1. When __remove_mapping() removes swapcache, __delete_from_swap_cache() > relies on memcg_data for the right counts to be updated; but that had > already been reset by mem_cgroup_swapout(). Swap those calls around - > mem_cgroup_swapout() does not require the swapcached flag to be set. > > 6.1 commit ac35a4902374 ("mm: multi-gen LRU: minimal implementation") > already made a similar swap for workingset_eviction(), but not for this. > > 2. memcg's "swapcached" count was added for memcg v2 stats, but displayed > on OOM even for memcg v1: so mem_cgroup_move_account() ought to move it. > > Fixes: b6038942480e ("mm: memcg: add swapcache stat for memcg v2") > Signed-off-by: Hugh Dickins Acked-by: Johannes Weiner